Discrete Io - Garmin GTX 3x5 Series Installation Manual

5.6.2 Altitude Gray Code Input
The parallel Gray code input can be used as a pressure altitude input.
ALT A1
ALT A2
ALT A4
ALT B1
ALT B2
ALT B4
ALT C1
ALT C2
ALT C4
ALT D4
GROUND (altitude Gray code ground)
The Gray code inputs are pulled down for active, or open for inactive.
The GTX 3x5 includes internal isolation diodes on the gray code inputs to prevent the unit from pulling the
encoder lines to ground when the transponder is turned off.
5.6.3 Altitude Input Selection Priority
Care must be taken to understand the priority for selecting the pressure altitude inputs. The GTX 3x5
searches the altitude inputs in a defined sequence and stops when it finds a valid pressure altitude input.

5.7 Discrete IO

EXT STANDY
ALTITUDE ALERT OUT
TEST MODE
EXT IDENT (momentary input)
AUDIO MUTE
AIR/GROUND
TIS-A SELECT
DISC IO1
DISC IO2
DISC IO
DISC IO
The discrete inputs and outputs are active low.
The discrete inputs are considered active if either the voltage to ground is ≤ 3.5 Vdc or the resistance to
ground is ≤ 375Ω. The inputs are considered inactive if the voltage to ground is > 6.5 Vdc or the resistance
to ground is > 100kΩ. If the input functions are not needed or not used, they should be left open.
190-01499-02
Rev. 1
Pin Name
Pin Name
Connector Pin
P3251 10
P3251 32
P3251 53
P3251 11
P3251 33
P3251 54
P3251 12
P3251 34
P3251 55
P3251 13
P3251 56
Connector Pin
P3251 14
P3251 17
P3251 35
P3251 36
P3251 37
P3251 57
P3251 58
P3251 15
P3251 16
P3252 13
P3252 14
GTX 3x5 TSO Installation Manual
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